There are a few methods of preparation of diazonaphthoquinonesulfonylchlorides reported in the literature and the same reports will be discussed below with merits and demerits.
The methods reported in prior art on the preparation of diazonaphthoquinonesulfonyl chlorides involves using chlorosulfonic acid and the corresponding diazonaphthoquinone sulfonic acid or its salt (CA, vol. 124, 32490e, PL 161,627, year 1993; CA vol. 64, 2033, USSR 173,756, year 1965; J.Prak.Chem., year 1991, vol. 333, p467). The main disadvantages of this method involves in using excess chlorosulfonic acid, reaction temperature and the evolution of gases like sulfurdioxide and hydrogenchloride.
Another method involves use of thionylchloride with dimethylformamide as catalyst with the corresponding diazonaphthoquinonesulfonic acid or its salt. This method also suffers the disadvantages like heating the reaction mixture, use of excess thionylchloride and evolution of sulfurdioxide and hydrogenchloride gases (CA, vol. 96, 34766b, Khim. Process, year 1981, p505 (Russ)).
Another method involves use of chlorosulfonic acid in combination with thionylchloride along with the corresponding diazonaphthoquinonesulfonic acid or its salt. The main disadvantages are the same as mentioned above (CA, vol. 105, 208620w, Ger (East) 272,511, year 1985 and DD 234,000, year 1986; CA vol. 112, 178384x, Ger (East) DD 269,846, year 1989, Ger (East) 312,180, year 1988; CA, vol. 124, 302642u, JP 08,27,098, year 1996; CA, vol. 125, 170873d, RO 104,624, year 1994).
Yet another method involves is the use of phosgene (toxic gas) with the corresponding diazonaphthoquinonesulfonic acid or its salt. This method has the optimum temperature conditions but the greatest disadvantage is the use of toxic phosgene gas (CA, vol. 102, 113031d, JP 59,196,860, year 1984; CA, vol. 105, 60439w, EP 178,356, year 1986).
The present invention describes an altogether new process for the preparation of diazonaphthoquinonesulfonylchlorides by reacting the corresponding diazonaphthoquinone sulfonic acid or its salt either with diphosgene or triphosgene in presence of triethylamine base in dichloromethane solvent. Various solvents like, chloroform, 1,2-dichloroethane, benzene, toluene, acetonitrile, benzonitrile, nitrobenzene and others are also used. Organic bases like tributylamine, pyridine, tripropylamine, N,N-dimethylaniline, N,N-diethylamine and other bases are also employed. Dichloromethane as solvent and triethylamine as organic base were preferred. The temperature of the reaction was varied over xe2x88x9250 to +5xc2x0 C. and xe2x88x9240xc2x0 C. is the preferred temperature condition. The base is found to be essential for the reaction to be conducted and without the organic base there is no reaction occurs. The 2 mole equivalent ratio of base is the right combination found. The work up procedure and isolation of the product diazonaphthoquinonesulfonylchloride is very simple and rapid. After the reaction the organic base and the solvent can be recovered. After the isolation of the product, the remaining filtrate contains the unreacted diazonaphthoquinonesulfonic acid as judged by the UV-Visible absorption data. The products were characterized by the spectral data.
Accordingly the present invention provides a process for the preparation of diazonaphthoquinonesulfonylchlorides of formula 1-3, using diphosgene or triphosgene which comprises 
reacting diazonaphthoquinonesulfonicacid sodium salt with an organic base in a molar ratio ranging between 1:1.5-1:2.5 in an organic solvent in the presence of diphosgene or triphosgene in a molar ratio of diazonaphthoquinonesulfonicacid sodium salt to diphosgene or triphosgene in the range of 1:1-1:1.5, at a temperature ranging from xe2x88x9250xc2x0 C. to 5xc2x0 C., for a period ranging from 40-90 min, subsequently increasing the temperature to 20-25xc2x0 C., removing the solvent and base from the above said reaction mixture under vacuum to obtain the yellow powder product and re-precipitating the desired product in ice water.
In an embodiment of the present invention the organic base used is selected from the group consisting of triethylamine, tributylamine, pyridine, tripropylamine, N,N-dimethylaniline and N,N-diethylamine.
In an another embodiment the organic base used is triethylamine.
In yet another embodiment the organic solvent used is selected from the group consisting of chloroform, 1,2-dichloroethane, benzene, toluene, acetonitrile, benzonitrile, nitrobenzene and dichloromethane.
In yet another embodiment the organic solvent used is dichloromethane.
In yet another embodiment the molar ratio of diazonaphthoquinonesulfonicacid sodium salt to organic base used is 1:2.
In yet another embodiment the molar ratio of diazonaphthoquinone sulfonicacid sodium salt to triphosgene or diphosgene used is 1:1.
In yet another embodiment A process as claimed in claim 1, wherein the reaction temperature used is xe2x88x9250xc2x0 C.
In yet another embodiment the diazonaphthoquinonesulfonicacid sodium salt used is selected from 2-Diazo-1-naphthoquinone-4-sulfonic acid sodium salt, 2-Diazo-1-naphthoquinone-5-sulfonic acid sodium salt and 1-Diazo-2-naphthoquinone-4-sulfonic acid sodium salt.
In yet another embodiment the diazonaphthoquinonesulfonyl chloride obtained is selected from 2-Diazo-1-naphthoquinone-4-sulfonylchloride of formula 1, 2-Diazo-1-naphthoquinone-5-sulfonulchloride of formula 2, and 1-Diazo-2-naphthoquinone-4-sulfonylchloride of formula 3.